Commentary on Vrabelova et al

The paper by Vrabelova et al. reflects a comprehensive genetic approach in characterizing genetically patients with Wilson disease (WD). They studied mutations within ATP7B-the gene encoding the defective WD protein ATPase 7B-in 227 WD patients from 200 unrelated Czech and Slovak families, which represents a very large cohort for WD, and therefore, the impact of their findings are highly important. There are accumulating papers published on mutations in WD, but besides reporting new mutations, mostly the genetic analysis is presented by sequencing data of limited exon analysis and the lack of additional screening techniques used. This in turn complicates the current interpretation of the reported mutations within ATP7B and the role of genetic testing for WD in general. The real distribution of mutations within ATP7B are not well established, there is limited information on the mutational detection rate, and there is still little known on the promoter region of ATP7B.     

Influence of acute exercise on human platelet responsiveness: possible involvement of exercise-induced oxidative stress

The aim of this study was to evaluate in sedentary male subjects the effects of an acute bout of strenuous and moderate exercise on ex vivo platelet responsiveness and its possible relationship with exercise-associated modifications of oxidant-antioxidant status. An increased ADP- and collagen-evoked platelet aggregation associated with modified membrane fluidity and ion homeostasis was observed after exhaustive exercise. After moderate exercise, we found a decrease of platelet aggregation evoked by low concentrations of agonists. Strenuous exercise, but not moderate exertion, resulted in the enhanced accumulation of secondary products of lipid peroxidation, decreased total antioxidant capacity, including a diminished superoxide dismutase activity, and increased susceptibility of low-density lipoprotein (LDL) to in vitro oxidation. Acute elevation of plasma nitrite/nitrate (NO_X) content was observed following each single session of physical test, whilst the platelet NO_X content was decreased after strenuous exercise and increased after moderate exercise. Findings of the present study suggest that oxidative stress induced by acute strenuous exercise may interfere with platelet responsiveness most likely by promoting oxidized LDL-mediated platelet activation and by decreasing plasma and platelet-derived nitric oxide (NO) bioactivity. Moreover, our results further suggest that platelet responsiveness following an acute moderate physical stressor may depend on the efficiency of plasma and intraplatelet NO to desensitize platelets to agonist stimulation. Electronic Publication     

L-精氨酸治疗不匀称型胎儿生长受限的临床观察

目的：观察L-精氨酸联合常规治疗对不匀称型胎儿生长受限的临床疗效，探讨一氧化氮在治疗不匀称型胎儿生长受限中的作用机制。方法：将66例不匀称型胎儿生长受限的孕妇分为常规治疗组（A组，36例）和L-精氨酸联合常规治疗组（B组，30例）；另30例正常孕妇为对照组（C组）；分别检测3组孕妇母血及脐血亚硝酸盐/硝酸盐（NO₂^-/NO₃^-）浓度、脐动脉血流波形、血液流变学指标及妊娠结局。结果：①治疗前A、B两组孕妇血NO₂^-/NO₃^- 浓度显著低于C组；②治疗后A、B两组孕妇血NO₂^-/NO₃^- 水平均明显增高，且B组高于A组（P<0.01）；治疗后B组脐动脉搏动指数、阻力指数及孕妇血粘度低切值明显低于治疗后A组（P<0.05）。③B组新生儿平均出生体重显著高于A组（P<0.01）；B组脐血NO₂^-/NO₃^- 水平显著高于A组。结论：一氧化氮不足与不匀称型胎儿生长受限的发生密切相关，L-精氨酸联合常规药物治疗不匀称型胎儿生长受限疗效明显优于常规治疗组。     

葛根素对糖尿病大鼠睾丸的保护作用

目的： 探讨葛根素对糖尿病大鼠睾丸的保护作用及其机制。方法：雄性SD大鼠随机分成6组：正常对照组,糖尿病模型组,葛根素高(160 mg·kg-1)、中(120 mg·kg-1)、低(80 mg·kg-1)剂量治疗组,氨基胍(100 mg·kg-1)治疗组;各组大鼠每天腹腔注射相应药物1次,正常对照组及糖尿病模型组腹腔注射等体积丙二醇。治疗12周后,透射电镜下观察睾丸的形态学改变,用生化、免疫学方法测定睾丸组织中一氧化氮（NO）、内皮素-1（ET-1）、降钙素基因相关肽（CGRP）、丙二醛（MDA)的含量及一氧化氮合酶（NOS）、诱导型NOS(iNOS)、超氧化物歧化酶(SOD)、Ca2+-ATPase、Na+-K+-ATPase的活性,采用RT-PCR检测睾丸组织内皮型NOS(eNOS)、iNOS、CGRP、ET-1、醛糖还原酶（AR）的基因表达水平。结果：糖尿病组大鼠睾丸组织电镜下主要见到支持细胞与曲细精管基底膜接触面减小、出现空泡,胞浆内内含物形成;NO、CGRP含量及SOD、Ca2+-ATPase、Na+-K+-ATPase活性和eNOS、CGRP mRNA表达明显低于正常对照组（P<0.05或P<0.01）,而ET-1、MDA含量及NOS、iNOS活性和iNOS、AR、ET-1 mRNA表达明显高于正常对照组（均P<0.01）。经葛根素治疗后,上述改变逆转,与糖尿病模型组比较差异显著（P<0.05或P<0.01）,电镜下睾丸组织的形态结构接近于正常组;而葛根素高、中、低剂量治疗组、氨基胍治疗组间差异无显著。结论：葛根素对糖尿病大鼠睾丸具有一定的保护作用,其机制可能与改善睾丸血供及减轻氧化应激损伤有关。     

Heme oxygenase and carbon monoxide initiate homeostatic signaling

Carbon monoxide (CO), a gaseous second messenger, arises in biological systems during the oxidative catabolism of heme by the heme oxygenase (HO) enzymes. Many biological functions of HO, such as regulation of vessel tone, smooth muscle cell proliferation, neurotransmission, and platelet aggregation, and anti-inflammatory and antiapoptotic effects have been attributed to its enzymatic product, CO. How can such diverse actions be achieved by a simple diatomic gas; can its protective effects be explained via regulation of a common signaling pathway? A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases. The consequences of this activation remain unknown but appear to differ depending on cell type and circumstances. The majority of studies reporting a protective role of CO focus on pathways initiated by the pathological stimulus (e.g., lipopolysaccharide, hypoxia, balloon injury, tumor necrosis factor α, etc.) and its consequential modulation by CO. What has been less studied is the manner in which CO exposure alone modulates the molecular machinery of the cell so that a subsequent stress stimulus will elicit a homeostatic response as opposed to one that is chaotic and disordered. CO potentially interacts with other intracellular hemoprotein targets, although little is known about the functional significance of such interactions other then the known targets including mitochondrial oxidases, oxygen sensors, and nitric oxide synthases. The earliest response of a cell exposed to low concentrations of CO is clearly an increase in reactive oxygen species formation that we define as oxidative conditioning. This has important consequences for inflammation, proliferation, mitochondria biogenesis, and apoptosis. Within this review, we will highlight recent research on the molecular events underlying the physiologic effects of CO—which lead to cytoprotective conditioning.     

Agmatine attenuates stress- and lipopolysaccharide-induced fever in rats

Physiological stress evokes a number of responses, including a rise in body temperature, which has been suggested to be the result of an elevation in the thermoregulatory set point. This response seems to share similar mechanisms with infectious fever. The aim of the present study was to investigate the effect of agmatine on different models of stressors [(restraint and lipopolysaccharide (LPS)] on body temperature. Rats were either restrained for 4 h or injected with LPS, both of these stressors caused an increase in body temperature. While agmatine itself had no effect on body temperature, treatment with agmatine (20, 40, 80 mg/kg intraperitoneally) dose dependently inhibited stress- and LPS-induced hyperthermia. When agmatine (80 mg/kg) was administered 30 min later than LPS (500 microg/kg) it also inhibited LPS-induced hyperthermia although the effect became significant only at later time points and lower maximal response compared to simultaneous administration. To determine if the decrease in body temperature is associated with an anti-inflammatory effect of agmatine, the nitrite/nitrate levels in plasma was measured. Agmatine treatment inhibited LPS-induced production of nitrates dose dependently. As an endogenous molecule, agmatine has the capacity to inhibit stress- and LPS-induced increases in body temperature.     

原发性高血压患者红细胞L-精氨酸/一氧化氮系统的改变

目的:探讨原发性高血压时人体红细胞L-精氨酸/一氧化氮系统的变化。方法:原发性高血压患者(EH)12例与健康成年人10例作对照,制备红细胞悬液,分别测定红细胞的一氧化氮(NO)产生量、红细胞一氧化氮合酶(NOS)活性、红细胞cGMP含量和L-精氨酸(L-Arg)转运的动力学特征。结果:原发性高血压患者红细胞NO产生量明显低于对照组(P<0.01),红细胞cGMP含量也少于对照组27.2%(P<0.05)。EH患者红细胞NOS活性仅为对照组的47.8%(P<0.01)。其L-精氨酸转运总能力与Y⁺载体转运系统的转运能力明显低于正常人(P<0.01),而Y⁺L载体转运系统的转运能力无明显改变(P>0.05)。L-精氨酸总转运的最大速率与Y⁺载体转运系的最大速率分别较对照组降低36.8%和42.5%(P<0.01),各组间米氏常数无差异。结论:原发性高血压患者红细\胞L-Arg/NOS/NO/cGMP系统存在明显异常。     

The CSF concentration of ADMA,but not of ET-1, is correlated with the occurrence and severity of cerebral vasospasm after subarachnoid hemorrhage

Under physiological conditions, vasoconstrictors and vasodilators are counterbalanced. After aneurysmal subarachnoid hemorrhage (SAH) disturbance of this equilibrium may evoke delayed cerebral vasospasm (CVS) leading to delayed cerebral ischemia (DCI). Most studies examined either the vasoconstrictor endothelin-1 (ET-1) or the vasodilative pathway of nitric oxide (NO) and did not include investigations regarding the relationship between vasospasm and ischemia. Asymmetric dimethyl-l-arginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), decreases the concentration of NO. Studies have correlated increasing concentrations of ADMA with the course and degree of CVS after SAH. We sought to determine, if ADMA and endothelin-1 (ET-1) are associated with CVS and/or DCI after SAH. CSF concentrations of ADMA and ET-1 were retrospectively determined in 30 patients after SAH and in controls. CVS was detected clinically and by arteriogaphy. DCI was monitored by follow-up CT scans. 17 patients developed arteriographic CVS and 4 patients developed DCI. ADMA but not ET-1 concentrations were correlated with occurrence and degree of CVS. However, ET-1 concentrations were correlated with WFNS grade on admission. Neither ADMA nor ET-1 correlated with DCI in this cohort. ET-1 concentrations seem to be associated with the impact of the SAH bleed. ADMA may be directly involved in the development and resolution of CVS after SAH via inhibition of NOS disturbing the balance of vasodilative and -constrictive components.     

The autophagy enhancer spermidine reverses arterial aging

Arterial aging, characterized by stiffening of large elastic arteries and the development of arterial endothelial dysfunction, increases cardiovascular disease (CVD) risk. We tested the hypothesis that spermidine, a nutrient associated with the anti-aging process autophagy, would improve arterial aging. Aortic pulse wave velocity (aPWV), a measure of arterial stiffness, was ～20% greater in old (O, 28 months) compared with young C57BL6 mice (Y, 4 months, P < 0.05). Arterial endothelium-dependent dilation (EDD), a measure of endothelial function, was ～25% lower in O (P < 0.05 vs. Y) due to reduced nitric oxide (NO) bioavailability. These impairments were associated with greater arterial oxidative stress (nitrotyrosine), superoxide production, and protein cross-linking (advanced glycation end-products, AGEs) in O (all P < 0.05). Spermidine supplementation normalized aPWV, restored NO-mediated EDD and reduced nitrotyrosine, superoxide, AGEs and collagen in O. These effects of spermidine were associated with enhanced arterial expression of autophagy markers, and in vitro experiments demonstrated that vascular protection by spermidine was autophagy-dependent. Our results indicate that spermidine exerts a potent anti-aging influence on arteries by increasing NO bioavailability, reducing oxidative stress, modifying structural factors and enhancing autophagy. Spermidine may be a promising nutraceutical treatment for arterial aging and prevention of age-associated CVD.     

维生素D3引起大鼠血管钙超载对血管L-精氨酸/NO途径的影响

目的：观察血管钙超载对Ｌ－精氨酸／ＮＯ途径的影响。方法：维生素Ｄ３（ＶｉｔＤ３）注射引起大鼠血管钙超载,检测血管ＮＯ生成、ｃＧＭＰ含量、Ｌ－瓜氨酸转化及Ｌ－精氨酸转运的变化,并与口服Ｌ－精氨酸治疗组大鼠比较。结果：大鼠血管钙含量（９４４±１８８）ｖｓ对照（１０７±１８）μｍｏｌ／ｇ干重,（Ｐ＜００１）,血管ＮＯ生成减少,组织ｃＧＭＰ含量降低,但Ｌ－瓜氨酸转化增高,Ｌ－精氨酸（Ｌ－Ａｒｇ）高和低亲和性转运的最大速率（Ｖｍａｘ）分别降低５０５％和４５８％（Ｐ＜００１）。口服Ｌ－Ａｒｇ治疗的大鼠血管ＮＯ生成和ｃＧＭＰ含量都较钙超载大鼠明显增高（Ｐ＜００１）,Ｌ－Ａｒｇ高、低亲和性转运的Ｖｍａｘ增加。结论：血管钙超载对Ｌ－Ａｒｇ／ＮＯ途径损伤的主要环节在Ｌ－Ａｒｇ的跨膜转运,补充ＮＯ前体Ｌ－Ａｒｇ可能减轻钙超载引起的血管损伤。     

Oxidonitrergic and antioxidant effects of a low molecular weight peptide fraction from hardened bean (Phaseolus vulgaris) on endothelium

About 3000 tons of beans are not used in human food due to hardening. Several studies on bean-derived bioactive peptides have shown potential to treat some diseases, including those relying on oxidative dysfunctions. We assessed the effects of peptides extracted from hardened bean Phaseolus vulgaris (PV) on reactive oxygen species (ROS) and nitric oxide (NO) production, cytotoxic and cytoprotective effects in endothelial cells, and oxidonitrergic-dependent vasodilating effects. Extract was composed by peptide fraction <3 kDa (PV3) from hardened common bean residue. PV3 sequences were obtained and analyzed with bioinformatics. Human umbilical vein endothelial cells were treated with 10, 20, 30, and 250 µg/mL PV3. Oxidative stress was provoked by 3% H₂O₂. Cytotoxicity and cytoprotective effects were evaluated by MTT assay, whereas, ROS and NO were quantified using DHE and DAF-FM fluorescent probes by confocal microscopy. NO- and endothelium-dependent vasodilating effects of PV3 were assessed in isolated aortic rings. We found 35 peptides with an average mass of 1.14 kDa. There were no cell deaths with 10 and 20 μg/mL PV3. PV3 at 30 μg/mL increased cell viability, while cytotoxicity was observed only with 250 μg/mL PV3. PV3 at 10 μg/mL was able to protect cells from oxidative stress. PV3 also increased NO release without causing cell death. It also reduced relative ROS production induced by H₂O₂. PV3 vasodilating effects relied on endothelium-dependent NO release. PV3 obtained from low-commercial-value bean displays little cytotoxicity and exerts antioxidant effects, whereas it increases endothelial NO release.     

Effects of aspirin plus alpha-tocopherol on brain slices damage after hypoxia-reoxygenation in rats with type 1-like diabetes mellitus

Diabetes mellitus is a risk factor for cerebrovascular ischemic disease. Aspirin (acetylsalicylic acid) is the most widely used drug for the secondary prevention of thrombotic phenomena. It has been also recently demonstrated that -tocopherol influenced in vitro the antiplatelet effect of aspirin. The aim of the present study is to evaluate the effects aspirin plus -tocopherol on cerebral oxidative stress, prostaglandin production and the nitric oxide pathway in a model of hypoxia-reoxygenation in rat brain slices. Our results show an imbalance in brain oxidative status (reflected mainly as the increase in lipid peroxides) as a result of diabetes itself rather than a failure of the glutathione-based antioxidant system. Moreover, our results also show a higher concentration of prostaglandins in the brain of diabetic animals and a higher nitric oxide concentration, mainly through a high iNOS activity. After 180 min of post-hypoxia reoxygenation, LDH activity was 40.6% higher in animals with diabetes, in comparison to non-diabetic animals. The increase of the LDH efflux observed in non-treated rats was reduced by 31.2% with aspirin, by 34.7% with -tocopherol and by 69.8% with the association aspirin--tocopherol. The accumulation of prostaglandin E₂ observed in diabetic non-treated rats was reduced statistically after the treatment with aspirin (34.2% inhibition), -tocopherol (19.3% inhibition) or the association aspirin--tocopherol (54.4% inhibition). Nitric oxide production after 180 min reoxygenation was significantly reduced in aspirin (36.4%), -tocopherol (22.7%) and aspirin--tocopherol (77.8%) treated rats with respect to diabetic non-treated animals; this was related mainly with a reduction in iNOS activity. The association between aspirin and alpha tocopherol could protects against brain ischemic-reperfusion damage with a better profile than aspirin alone.     

牛磺酸对果糖诱导的高血压胰岛素抵抗大鼠红细胞L-精氨酸/一氧化氮途径的影响

目的和方法:在4%果糖引起大鼠胰岛素抵抗高血压模型上,观察红细胞L-精氨酸(L-Arg)/一氧化氮(NO)途径的改变,并观察牛磺酸对其改变的影响。结果:饮用果糖大鼠血压、血糖、血浆胰岛素水平明显高于对照大鼠的同时,红细胞对L-Arg总的转运及Y⁺载体转运的最大转运速率(V_max)分别低于对照大鼠31%和37％(P＜0.01);米氏常数(Km)分别比对照大鼠高35%和30%(P＜0.01)。红细胞内一氧化氮合酶(NOS)活性、cGMP水平和血浆NO含量明显低于对照大鼠(P＜0.01)。应用牛磺酸治疗可明显逆转上述改变(P＜0.01)。结论:胰岛素抵抗高血压大鼠存在有红细胞L-Arg/NO系统的功能障碍,牛磺酸可显著提高红细胞对L-Arg的转运速率和NOS活性。     

L-精氨酸对原发性高血压影响的临床研究

目的:从血流动力学及神经内分泌学两方面探讨左旋精氨酸(L-Arg)-一氧化氮(NO)通路对原发性高血压的影响。方法: 选择24例高血压病人随机分为两组,一组静滴L-Arg ,一组静滴生理盐水,观察其血压、心率及心功能,同时检测血浆中NO、血管紧张素Ⅱ(AngⅡ)、内皮素(ET)、血栓素A₂(TXA₂)以及前列环素(PGI₂)以探讨其降压机理。 结果:L-Arg治疗后,病人血压下降、心率增快,心输出量(CO)、每搏输出量(SV)、射血分数(EF)增加,总外周阻力(TPR)降低,血浆NO、PGI₂含量升高,ET、AngⅡ、TXA₂水平降低。静滴80 min时,随NO浓度降低CO、SV、EF也随之降低,而TPR又回升,血浆ET、AngⅡ发生相应变化,TXA₂、PGI₂无明显改变。结论:L-Arg通过直接升高血浆NO水平引起血流动力学改变,通过间接反馈效应改变ET、AngⅡ水平,并可抑制血小板聚集。     

吡咯烷二硫代氨基甲酸酯对2型糖尿病大鼠肾脏的保护作用

目的: 探讨吡咯烷二硫代氨基甲酸酯(PDTC)对2型糖尿病大鼠肾脏的保护作用及其机制。方法: 雄性Wistar大鼠,随机分为2组:正常对照(NC)组和高脂饮食(HFD)组。喂养8周后高脂饮食组大鼠腹腔注射小剂量链脲佐菌素(STZ, 27 mg/kg),以随机血糖≥16.7 mmol/L为2型糖尿病大鼠造模成功。将成模大鼠随机分为2组:糖尿病模型(DM)组和PDTC (50 mg·kg^-1·d^-1, ip)治疗组。治疗1周后断头处死大鼠,留取各组血浆、尿液及肾脏标本。测定各组血糖、尿微量白蛋白/肌酐比值、肾皮质组织中丙二醛(MDA)的含量、超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)的活性;经HE及Masson染色观察大鼠肾小球形态学变化;透射电镜观察肾脏微血管超微结构改变;免疫组化观察肾脏组织中诱生型一氧化氮合酶(iNOS)和硝基酪氨酸(NT)的表达。结果: PDTC治疗组血糖和尿微量白蛋白/肌酐比值较DM组明显降低(P<0.01)。DM组肾皮质组织中MDA含量明显高于NC组, GSH-Px和SOD的活性明显低于NC组(P<0. 05) 。HE及Masson染色显示,DM组肾小球体积增大,肾小管扩张,系膜区扩张,Masson染色阳性物质增多,提示肾小球毛细血管基底膜增厚;PDTC治疗组病理改变较DM组明显改善。电镜超微结构显示,DM组基底膜高度增厚,厚度不均,有断裂层,足突融合;PDTC治疗组基底膜轻度增厚,足突轻度融合。免疫组化显示,DM组iNOS和NT表达量较NC组明显增多(P<0.05);PDTC治疗组iNOS和NT表达量较DM组明显减少(P<0.05)。结论: PDTC不仅具有降低血糖作用,而且可通过减少iNOS和NT表达改善糖尿病肾脏损害。     

NG-硝基-L-精氨酸对大鼠内毒素性肺线粒体损伤的影响

目的： 观察非选择性一氧化氮合酶(NOS)抑制剂NG-硝基-L-精氨酸(L-NA)对急性肺损伤大鼠肺线粒体功能的影响，并探讨其改善急性肺损伤的作用机制。方法: 将SD大鼠随机分为空白对照组、急性肺损伤组、L-NA治疗组，采用舌静脉注射脂多糖(LPS)复制大鼠急性肺损伤模型，于大鼠急性肺损伤3h后给L-NA治疗3h，断头放血处死大鼠，迅速取出肺脏，匀浆器混匀后，低温差速离心法提取肺线粒体，测定线粒体总ATP酶、超氧化物歧化酶（SOD）、谷胱甘肽过氧化物酶（GSH-Px）、总一氧化氮合酶（T-NOS）、诱生型一氧化氮合酶（iNOS）、结构型一氧化氮合酶（cNOS）的活性，以及线粒体肿胀度、膜流动性和线粒体一氧化氮（NO）、丙二醛（MDA）含量；电镜观察大鼠肺线粒体超微结构的改变及治疗药对此改变的影响。结果: 在大鼠内毒素性急性肺损伤后，肺脏组织中线粒体表现为肿胀、膜流动性降低，线粒体中的T-NOS和iNOS活性显著升高，线粒体NO生成明显增加，而cNOS活性无明显变化；线粒体总ATP酶、SOD、GSH-Px活性均明显下降，线粒体MDA含量明显升高。急性肺损伤3h给予L-NA治疗3h,与急性肺损伤组相比，一氧化氮合酶活性有所改变，NO生成显著下降，总ATP酶、SOD、GSH-Px活性均显著升高，MDA含量下降。电镜结果显示内毒素性急性肺损伤后肺脏组织细胞水肿，线粒体肿胀、嵴断裂、溶解、消失；L-NA能改善内毒素性急性肺损伤引起的细胞水肿、线粒体肿胀和空泡化。结论: L-NA能明显抑制急性肺损伤后线粒体一氧化氮合酶活性，减少NO生成，改善线粒体能量供应，增加线粒体抗氧化作用，从而减轻急性肺损伤。     

碱性成纤维细胞生长因子对兔血管舒张功能及左旋精氨酸/一氧化氮途径的影响

目的：本文观察了碱性成纤维细胞生长因子（ｂＦＧＦ）对离体主动脉舒张反应,一氧化氮（ＮＯ）生成及左旋精氨酸（Ｌ－Ａｒｇ）转运的影响。方法：离体大鼠主动脉环测定张力,主动脉薄片孵育测定ＮＯ生成和Ｌ－精氨酸（Ｌ－Ａｒｇ）转运。结果：ｂＦＧＦ呈剂量依赖性地诱导血管内皮依赖性舒张,增加血管低亲和Ｌ－Ａｒｇ的最大转运速度（与对照组比较增加４５％,Ｐ＜０．０１）,显著增加ＮＯ的产生（比对照组增加４３％）。结论：ｂＦＧＦ可增加Ｌ－Ａｒｇ转运,对内皮衍生舒张因子／一氧化氮（ＥＤＲＦ／ＮＯ）系统具有重要的调节作用